The National Institute for Occupational Safety and Health (NIOSH)NIOSH Mining

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Research Summary

Specify locations and protocols for implementing continuous ventilation monitoring along the shield line to provide early detection of gas exchanges between face and gob, and thus improve a mine's ability to monitor and control ventilation and methane concentrations around the face.

Longwall mining presents a particularly complex ventilation challenge—not only are large quantities of methane gas liberated during mining, but large methane reservoirs are created concurrently. This necessitates constant vigilance on the part of mine operators to maintain ventilation. Poor or incomplete caving may allow face air to preferentially flow behind the shield line in larger quantities than usual, resulting in a decrease of critical ventilation air to dilute harmful dust and hazardous gases. This condition is magnified in the case of wider faces, where increased flow resistance may enhance the frequency and magnitude of such airflow movements.

In this project, field studies will be conducted at operating longwalls to quantify ventilation airflow levels and methane gas concentrations along the longwall face and behind the shield line. Such data can indicate the degree to which airflow degrades for tightly or loosely caved gobs, and can reveal a potential for gas migration out of the gob. These data will be used to calibrate numerical models to locate regions for potential exchanges of airflow/methane between the gob and the face. The modeling will quantify the void volumes in regions immediately behind the shields using relative porosity values, and will quantify their impacts on movements of airflow/methane between the face and gob. Model results will be used to develop potential locations for continuous monitoring of airflow/methane along the face, with the efficacy of these locations verified through subsequent underground evaluations.

Acquisition of relevant longwall field data at multiple mine sites remains the primary focus of this work. However, it is understood that considerable difficulties and sensitivities are associated with acquiring and measuring field data of this type. In the event that NIOSH cannot find suitable cooperating mines or needs to generate complementary monitoring data, a physical scaled longwall model has been designed, built, and has undergone baseline testing. When field testing is conducted at new sites, these three tasks can be used to complement each other. Field calibrations can enhance both the numerical and physical models. Ventilation scenarios difficult to produce in the field can be addressed through simulations that can portray and expand on the field measurements. Ventilation studies at mine sites have been completed and new experiments are in the planning phase.